Evaluation Plan for Passive Debris Cooling System and Refractory Layer

摘要

In the event of a severe accident, it is necessary to prevent the release of radioactive materials into the environment due to damage to a containment vessel. It is also important to mitigate the consequences of such a severe accident. If debris falls down from a reactor vessel onto a pedestal floor, concrete will be eroded by the debris as a result of thermal decomposition and fusion. After continuous erosion, the pedestal may be damaged or a steel liner of the boundary may be penetrated. In addition, concrete decomposition will cause the production of non-condensable gases such as hydrogen and carbon monoxide, resulting in pressurization of the containment vessel. Therefore, we have been developing a safety system to stabilize the core melt and avoid a molten core concrete interaction (MCCI). Although water will be injected into the debris cooling system, it is difficult to hold high-temperature debris at about 2500 K. Heat-resisting materials with high melting points should be installed. The heat-resisting materials can protect the concrete or components of the system (like the core-catcher) against short-term thermal impingement and long-term erosion after water injection. We completed primary screening of heat-resisting materials in 2012 and investigated a eutectic reaction with oxide components in debris/corium and an oxidation-reduction reaction with metal components in corium.